1. Field of the Invention
The present invention generally relates to the pumping of loose materials and, more particularly, is concerned with an apparatus and method for metered infeeding, compacting as required, and pumping coarse material of low fluidity.
2. Description of the Prior Art
A wide variety of materials are difficult to move by pumping for feeding these materials in their respective processing operations. These materials range from low-density materials requiring substantial pre-compression to higher-density material requiring little or no pre-compression. The low-density materials are typically bulky, fibrous or stringy, non-frangible, tough, non-fluid, wet or dry materials. An example of such low-density materials is feathers. The higher-density materials are typically coarse, lumpy, frangible or non-frangible, semi-fluid, heterogeneous, wet or dry materials. Representative examples of such higher-density materials are ground offal and wet hog hair.
One example of a process involving low-fluidity, low-density material requiring pre-compression is the steam hydrolyzation of feathers. One of the two continuous hydrolyzing systems in current use is exemplified by the hydrolyzing system disclosed in U.S. Pat. No. 3,617,313 to Harrington et al. This system employs an infeed pump which includes a variable-pitch screw that compresses feathers into a pressure-sealing plug, then ejects them into a pressurized mildly agitated hydrolyzing retort. The pump is dependent on the tightly knit compressed wad of feathers for the formation of the self-sealing plug. Since the screw is not a positive-displacement device, it loses its seal when liquid or plastic materials (often present in feathers) enter the pump. Blow-back that depressurizes the retort then occurs through the pump. As a result, the operation of the system is frequently interrupted, usually requiring shutdown and, often, disassembly for clean-out.
Also, in this system, the high-pressure squeezing action of the screw "wrings" free water out of the feathers, to the degree that live steam must be injected into the hydrolyzing retort in order to build adequate hydrolyzing pressure and supply the water needed for the hydrolyzing reaction. The injection of steam is very expensive because it is not returned to the boiler.
The other of the two continuous hydrolyzing systems in current use is exemplified by the hydrolyzing system disclosed in U.S. Pat. Nos. 4,231,926, 4,286,884, 4,378,311 and 4,497,733 to Retrum. This system employs two vigorously-agitated retorts and an intermediate pump. In the first non-pressurized retort of this system, the feathers are beaten to a coarse pulp at the atmospheric saturation temperature of water. The coarse pulp is then pumped via the intermediate pump into a second pressurized vigorously-agitated hydrolyzing retort. This system requires two vigorously-agitated retorts and a pump, which are expensive. This system is more economical in large installations than in the small installations which constitute most of the market.
Consequently, in view of the problems associated with the two currently-used continuous hydrolyzing systems, a need still exists for improvements in pumping difficult materials.